Castaic residents may soon see their library double in size as Los Angeles County supervisors are scheduled to decide Tuesday if they want to approve a $3.59 million expansion project.

Under the proposal, the existing 6,985-square-foot library would have an additional 5,247 square-feet of space added, along with new books, materials, furniture, fixtures, equipment, telephones and data systems, according to a report prepared by the Los Angeles County Chief Executive Office.

The library — at 27971 Sloan Canyon Road — would total 12,232 square feet when construction was completed, according to the report.

Although the cost of the expansion would total $3.59 million — with a large portion of that used for the lease with Castaic FCG Properties — the county would also have an option to purchase the property for an additional $2.35 million after the improvements are completed, said Lori Glasgow, deputy to Supervisor Michael D. Antonovich.

The county has been looking at expanding the Castaic Library since last year, Glasgow said. The new area would add a community room, study areas and reading areas to the library.

Most of the major modifications to the library have already been made, and the expansion would mean the library would take up the entire upper level of the building if its approved by supervisors, Glasgow said.

The expansion would be funded with $1.87 million from the public library’s developer fee budget and the transfer of $2.14 million in net county cost from Stevenson Ranch Library, according to the report.

Despite the county’s plans for the Castaic Library, the county still wants to build a library in Stevenson Ranch, said Tony Bell, spokesman for Antonovich.

“We absolutely have every intention of still building a library in Stevenson Ranch,” Bell said, adding that the county is still looking for a site for a Stevenson Ranch library.

If Tuesday’s expansion plan is approved, the county expects to have construction completed by next spring for the grand opening of the Castaic Library, Glasgow said.